No UV coordinates Substance Painter
I had similar problem.

So i had done the mesh in Blender, and UV unwrapped it as well. Export, and same error in Substance Painter.

Solution was to while you export in Blender, be sure to check the Selected Object, and prior to choosing File > Export, be sure to either select all objects in the scene you want exported in the OBJ/FBX file, or delete everything else in the scene.

As I understand it, when you export the FBX or OBJ in Blender, it takes every single item in the scene (meshes, hidden meshes, cameras, stuff like that), and while you have the mesh you wanted to put in Substance Painter, you have all the other objects there as well.

In my case, I had some duplicates on separate layer for "backups", which came with the FBX into Substance Painter, even though I chose the mesh in Blender 3D viewport, I didn't have the Selected Objects checked in export properties.